Vehicular drive system and driving method

ABSTRACT

In a shift system wherein the transfer of power is performed using a motor, the smaller the gear ratio difference is, the smaller can be made the motor output. However, the number of gears must be increased in order to reduce the gear ratio. As the number of gears increases, the problem of gear noise becomes more serious. It is necessary to prevent both an increase in the number of gears and an increase of the motor output. In a vehicular drive system according to the present invention, a shifting power unit is not merely provided between a first intermediate shaft and a second intermediate shaft of a shift system which has the two intermediate shafts, but one side of a shifting power unit is connected to a vehicle driving power unit, while an opposite side thereof is connected to a power transfer switching clutch so as to be connected to the first or the second intermediate shaft through a reduction mechanism, whereby the output of the shifting power unit is decreased while minimizing an increase in the number of gears.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 11/002,140.

CLAIM OF PRIORITY

The present application claims priority from Japanese application serialno. 2003-405310 filed on Dec. 4, 2003, the contents of which are herebyincorporated by reference into this application.

BACKGROUND OF THE INVENTION

The present invention relates to an automatic transmission, an automatictransmission control device, an automatic transmission control method,an automatic shift system, and a vehicle using the same.

As a conventional automatic transmission there is used a planetary geartype or parallel-shaft type shift mechanism and there usually is adopteda method wherein a shift is performed by selectively engaging clutchesprovided individually in gear shift ranges of different transmissiongear ratios (see, for example, Japanese Patent Laid-Open No.H10(1998)-89456). The applicant in the present case has proposed such asystem as shown in Japanese Patent Application No. 2002-3561245 whereina parallel-shaft type shift mechanism having two input shafts iscombined with a motor to perform a shift actively.

In the system shown in the above application 2002-3561245, gear trainsare arranged on two input shafts so as be different in gear ratio todecrease a change in rotation during a shift, whereby the output of ashifting power unit can be decreased. According to this construction,however, the number of gears used becomes twice as large, with aconsequent likelihood of an increase of gear noise, mass, and weight.

If the number of gears used is decreased, the output of the shiftingpower unit will increase.

Further, in the application 2002-3561245, for starting a vehicle drivingpower unit by the shifting power unit, it is absolutely necessary toengage any of gears connected to an output shaft. Thus, a starting shockis transferred to the vehicle.

SUMMARY OF THE INVENTION

It is an object of the present invention to eliminate theabove-mentioned inconveniences and provide a vehicular drive systemwhich provides a high economical effect.

The vehicular drive system of the present invention is characterized inthat a shifting power unit is not merely provided between an input shaftand an intermediate shaft, but a mechanism for transferring of powerfrom the input shaft to both first and second intermediate shafts andfor cutting off the power is provided; one side of the shifting powerunit is connected to the input shaft, while an opposite side thereof isconnected to a power transfer switching clutch; and the shifting powerunit is connected to the first or the second intermediate shaft througha reduction mechanism. Thereby, the output of the shifting power unitcan be decreased while minimizing an increase in the number of gears.

According to the present invention, a gear ratio different from that ofreduction gears in a transmission is provided in common, whereby thenumber of gears used can be decreased without increasing the capacity ofa motor which is high in cost, and thus a more outstanding economicaleffect can be obtained.

Moreover, since the shifting power unit is provided between the first orthe second intermediate shaft and the input shaft, a vehicle drivingpower unit can be started without engaging a gear connected to an outputshaft and hence there can be attained a highly quiet drivability withouttransfer of a starting shock to the vehicle.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a construction diagram a vehicular drive system according to afirst embodiment of the present invention;

FIG. 2 is a morphological diagram showing a mounted state of thevehicular drive system of FIG. 1 on an automobile;

FIG. 3 is a construction diagram related to a control system shown inFIG. 1;

FIG. 4 shows a torque transfer path at the time of start-up of an enginein FIG. 1;

FIG. 5 is a flowchart of a control system in an up-shift;

FIG. 6 shows changing torque transfer paths and operations of clawclutches in an up-shift;

FIG. 7 is a time chart of torque and the number of revolutions in anup-shift;

FIG. 8 is a flowchart of the control system in a down-shift;

FIG. 9 shows changing torque transfer paths and operations of clawclutches in a down-shift;

FIG. 10 is a time chart of torque and the number of revolutions in adown-shift;

FIG. 11 shows changing torque transfer paths and operations of clawclutches in a jump shift;

FIG. 12 shows a second embodiment of the present invention; and

FIG. 13 shows a third embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a construction diagram showing a first embodiment of thepresent invention. A vehicle driving power unit 1 is coupled to an inputshaft 300 of a transmission 2. The vehicle driving power unit 1 isgenerally an internal combustion engine, but may be a power unit havinga rotary shaft such as a motor. An output shaft 3 of the transmission 2is connected to wheels (not shown). With a dog clutch 103, the inputshaft 300 can transmit a driving force to a first intermediate shaft 13and a second intermediate shaft 17 and cut off the supply of the drivingforce. When the intermediate shaft 13 is selected, it is engaged to theinput shaft through a direct-coupling gear 101, while when theintermediate shaft 17 is selected, it is engaged to the input shaftthrough a direct-coupling gear 102. With shift gears 14, 15, 16, 18, 19,and 20, the first and second intermediate shafts are connected to theoutput shaft 3 through dog clutches 21, 22, and 23.

The above dog clutches are connected to shift actuators 25, 26, 27, 29,and 30, so that they can be engaged and disengaged with the drivingforce of the actuators. The actuators are usually automatic device suchas a motor type or a hydraulic pressure type. Since the dog clutches andthe actuators are of known techniques, detailed descriptions thereofwill here be omitted.

The input shaft 300 is connected to one shaft of a shifting power unit200. The other shaft of the shifting power unit 200 is connected to thefirst and second intermediate shafts 13, 17 through a dog clutch 113 andfurther through motor gears 111 and 112. This construction is a featureof the present invention. In this embodiment, though an electric motoris used as the shifting power unit 200, it may be substituted by afriction clutch. That is, the shifting power unit 200 is not speciallylimited insofar as it has two shafts and can transfer or generate power.

The shifting power unit 200 is constituted by an electric motor 5 and aplanetary gear mechanism 31. A rotary shaft of the motor is connected toa planetary gear in the planetary gear mechanism. The input shaft isconnected to a sun gear and a ring gear is connected to a switchingsleeve side of the dog clutch 113. Thereby the power of the motor isprovided to the input shaft and the first or second intermediate shaft.As a result, the power of the motor acts in opposite directions on theinput shaft side and on the first or the second intermediate shaft side.For example, if the connection is set so as to increase the rotationalspeed of the input shaft when the motor generates a positive torque, thetorque provided to the intermediate shaft side acts to lower therotational speed of the intermediate shaft. When an electric motor usedis of a construction permitting rotation of both stator and rotor, themotor alone may be installed as in an equivalent construction of FIG. 1.

FIG. 2 is a diagram showing a state in which the vehicular drive systemof the present invention is mounted on an automobile. The transmission 2is connected to the vehicle driving power unit 1. The output shaft 3drives 5 wheels 4 through a differential gear. The motor 5 is installedwithin the transmission 2. A motor controller 7 is connectedelectrically to the motor 5 and a battery 6 as a power supply of themotor controller 7 is mounted on the automobile. Many automobiles employa lead storage battery, but in the system of the present invention thenumber of times of charge and discharge is large, thus causingdeterioration of the battery. In the system, since charge and dischargeare sure to occur during a shift, there is little change in the amountof stored electricity before and after the shift. Thus, it is alsopossible to use a capacitor of a large capacitance which has recentlybeen marketed. If the capacitance stored and the capacitance outputtedare sufficient, as the mounting method of the capacitance, either ofmounting the capacitor in parallel with the battery and mounting italone is good enough.

An electronic controlled throttle valve 10 is provided in the vehicledriving power unit 1, whereby the output of the vehicle driving powerunit 1 can be controlled in accordance with a request signal.

A shift controller 8 not only controls the torque and the number ofrevolutions of the motor 5 through the motor controller 7 but alsocontrols the output of the vehicle driving power unit 1 through avehicle driving power controller 9 and further through the electroniccontrolled throttle valve 10. Further, the shift controller 8 commandsthe operation of the shift actuators 25 to 27 and 29 to 30.

FIG. 3 shows a control system in the case of using a motor as theshifting power unit 200. For example, the motor 5 is a permanent magnetsynchronous motor and is supplied with three-phase alternating currentsU, V, W by the motor controller 7. High-speed switching elements 39 areprovided respectively in three-phase arms of an inverter of the motorcontroller 7 to convert a direct-current voltage from the battery 6 to athree-phase alternating current of a variable frequency. Upon receipt ofa torque command and a number-of-revolutions command from the shiftcontroller 8, an inverter controller 38 not only controls a currentpassing rate of the inverter but also feeds back the output of currentsensors 40 in each arm and the output of a rotor angle detectingposition sensor 41 and makes control so that the torque and the numberof revolutions of the motor 5 become respective commanded values. Such acontrol is publicly known in the field of power electronics andtherefore a detailed explanation thereof will here be omitted.

FIG. 4 shows engaged positions of dog clutches for starting an internalcombustion engine (merely “engine” hereinafter) and a torque transferpath in the case of using the engine as the vehicle driving power unit1.

In FIG. 4(a), the first intermediate shaft is fixed by engaging dogclutches 21 and 22 simultaneously, and when the dog clutch 113 isengaged with the first intermediate shaft, all the torque is applied tothe engine 1. Therefore, if torque is applied in the starting directionof the engine 1, the engine begins rotating and becomes rotatable foritself.

With gears on the output shaft thus engaged, however, it is impossibleto completely eliminate such a vibration factor as backlash even if thefirst intermediate shaft is fixed. In the present invention, if a torquetransfer path which circulates between the motor 5 and the engine 1 isformed as in FIG. 4(b), it is possible to start the engine even withoutengagement of gears on the output shaft. This principle utilizes thefact that the torque applied to the input shaft 300 differs due todifferent gear ratios of both shafts of the shifting power unit 200. Oneshaft of the shifting power unit 200 is directly coupled (gear ratio1:1) to the input shaft, while the other shaft is connected through thegear 111 to the input shaft. Therefore, if the gear ratio of the gear111 is 1.4 for example, the difference becomes 1.4−1=0.4. Thus, if 100Nm is applied as the motor torque, 40 Nm torque is applied to the inputshaft and the engine begins to start up. With a torque of about 50 Nm atan ordinary temperature, engine can start. It follows that theapplication of 125 Nm suffices as the motor torque.

FIG. 5 is a flowchart of the control system in up-shift. With 1→2 powerON up-shift as an example, a gear switching state and a state of torquetransition are shown. In FIG. 6, changing torque transfer paths andoperations of claw clutches (mesh type clutches) are shown incorrespondence to steps in FIG. 5. FIG. 7 is a time chart of torque andthe number of revolutions in various portions.

While the automobile is running with the low gear 14 engaged, the motorspeed is controlled in Step 1 a, then in Step 1 b the motor speed ischanged until the relation between the engine speed Ne and the number ofrevolutions Na of the second intermediate shaft is determined to be in asynchronized state. In Step 1 c, the dog clutch 113 is operated toengage the gear 112.

Next, in Step 2 a the motor speed is controlled, then in Step 2B themotor speed is changed until determination of a synchronous state of thesecond gear 18. With the second gear 18 engaged in Step 2 c, the motor 5races at a motor speed of (N1−N2).Since N2=G1.5×No  (Eq. 1)N1=G1×No  (Eq. 2),N1>N2 and (N1−N2) takes a positive value. In Eq. 1, G1.5 stands for theproduct of gear ratios of the second gear 18 and the motor gear 112, andG1 stands for a gear ratio of the low gear.

If the motor torque is increased in a negative direction (a direction inwhich the torque serves as a driving force for the output shaft and as aload for the engine) in Step 3 a, an input torque of the second gearincreases, while that of the low gear decreases. This is a torquetransition process called torque phase.

In the torque transition, which is from the intermediate shaft 13 to theintermediate shaft 17, since the value of the motor torque Tm is madenegative, an input torque T2 of the second gear 18 increases, while aninput torque T1 of the low gear 14 decreases, and when the motor torqueTm reaches −Te, T1 becomes equal to zero and T2 equal to Te.

In Step 3 b, the shift controller 8 determines the end of torque phase,that is, determines that the input torque of the low gear 14 is zero.However, since in many cases it is impossible to detect a gear inputtorque directly, a value (Tm=|Te|) obtained when an actual motor torquehas become equal to the absolute value of the engine torque can beregarded as the gear input torque being zero. In this case, it isnecessary that the engine torque Te be determined beforehand bydetection or by calculation. A concrete method for the detection or thecalculation is disclosed in Japanese Patent Laid-Open Nos.H5(1993)-240073 and H6(1994)-317242 and therefore an explanation thereofwill here be omitted.

In Step 3 c, the low gear is disengaged. Since T1=0, the low gear can bedisengaged easily without any change in the operation of thetransmission. The direct-coupling gear 101 is also disengaged for directcoupling to the second gear.

Upon disengagement of the low gear, the engine speed becomes changeable.

When the shift controller 8 issues a motor speed change command in Step4 a, the engine speed changes toward an input number of revolutions ofthe second gear. This is a revolutions transition process called inertiaphase.

In the case of 1→2 up-shift, if the motor speed is decreased whilemaintaining Tm=−Te, the motor speed drops, then the rotational directionreverses and the motor speed rises in a negative direction.

In Step 4 b, the shift controller 8 determines the end of inertia phaseby detecting a synchronized state of the engine speed with the inputnumber of revolutions of the subsequent gear.

In Step 4 c, the shift controller 8 operates the dog clutch 103 toengage the direct-coupling gear 102. Because of the synchronized state,the gear 102 can be engaged easily without causing any change in theoperation of the transmission.

In Step 5 a, the shift controller 8 issues a motor torque decreasingcommand, making the motor torque zero, whereupon the engine torque Tewhich has been transferred to G1.5 through the motor 5 shifts to thesecond gear.

In Step 5 b, the shift controller 8 determines the end of the secondtorque phase by detecting that the motor torque Tm is zero.

In Step 5 c, the shift controller 8 disengages the motor gear 112 andterminates the shift. Since Tm is zero, the motor gear can be disengagedeasily without causing any change in the operation of the transmission.

FIG. 8 is a flowchart of the control system in pedal depressingdown-shift. FIG. 9 shows changing torque transfer paths and operationsof claw clutches, for example in the case of 2→1 down-shift. FIG. 10 isa time chart of torque and the number of revolutions in variousportions.

While the automobile is running with the second gear engaged, the motorspeed is controlled in Step 1 a and is changed in Step 1 b until asynchronized state of the motor gear 112 is determined.

When the motor gear 112 engages in Step 1 c, the motor 5 races at amotor speed of (N1−N2).Since N2=G1.5×No  (Eq. 3)N1=G2×No  (Eq. 4),N1<N2 and (N1−N2) takes a negative value.

If the motor torque is increased in a negative direction (a direction inwhich the torque serves as a driving force for the output shaft and as aload for the engine) in Step 2 a, an input torque of the low gearincreases, while that of the second gear decreases. This is a torquetransition process called torque phase.

In the torque transition, which is from the intermediate shaft 17 to theintermediate shaft 13, the motor torque is increased in the negativedirection, the input torque T2 of the low gear 14 increases, the inputtorque T1 of the second gear 18 decreases, and when the motor torque Tmreaches −Te, T1 becomes equal to zero and T2 equal to Te.

In Step 2 b, the shift controller 8 determines the end of torque phase,that is, determines that the input torque of the second gear 18 is zero.However, in the case where the input torque of the gear cannot bedetected directly, the determination can be done by detecting that theactual motor torque is equal to the absolute value of the engine torque(Tm=|Te|).

In Step 2 c, the shift controller 8 makes the dog clutch 103 operate todisengage the direct-coupling gear 102. In Step 3 a, the shiftcontroller 8 makes the dog clutch 103 further operate to engage thedirect-coupling gear 101. With T1=0, the disengagement can be doneeasily without causing any change in the operation of the transmission.

Upon disengagement of the direct-coupling gear 102, the engine speedbecomes changeable.

When the shift controller 8 issues a motor speed change command in Step4 a, the engine speed changes toward an input number of revolutions ofthe low gear. This is a revolutions transition process called inertiaphase.

In the case of 2→1 down-shift, if the motor speed is increased whilemaintaining Tm=−Te, the motor speed increases, then the rotationaldirection reverses and the motor speed rises in the positive direction.

In Step 4 b, the shift controller 8 determines the end of inertia phaseby detecting a synchronized state of the engine speed with the inputnumber of revolutions of the subsequent gear.

In Step 4 c, the shift controller 8 operates the dog clutch 22 to engagethe low gear 14. Because of the synchronized state, the low gear 14 canbe engaged easily without causing any change in the operation of thetransmission.

In Step 5 a, the shift controller 8 issues a motor torque decreasingcommand, making the motor torque zero, whereupon the engine torque Tewhich has been transferred to the motor gear 112 through the motor 5shifts to the low gear 14.

In Step 5 b, the shift controller 8 determines the end of the secondtorque phase by detecting that the motor torque Tm is zero.

In Step 5 c, the shift controller 8 operates the dog clutches 113 and 23to disengage the motor gear 112 and the second gear 18 and terminatesthe shift. Since Tm is zero, both gears can be disengaged easily withoutcausing any change in the operation of the transmission.

Reference has so far been made to 1-2 up-shift and 2-1 down-shift, butin the case of performing 1-2 up-shift, the shift can be performed inaccordance with the 2-1 down-shift procedure. Conversely, whenperforming 2-1 down-shift, the 1-2 up-shift procedure may be adopted.However, at certain gear ratios of the motor and the first and secondintermediate shafts, the motor output cannot be decreased if the shiftis performed in accordance with the said reverse procedure. In short,although the shift can be performed no matter which of the motor gears111 and 112 may be selected, the motor output during a shift can bedecreased to a maximum of one half if the product of gear ratios of themotor gear selected and a shift gear during a revolutions transition isset so as to lie between the gear ratios before and after the shift. Anexplanation of this point will now be given using actual numericalvalues. For example, it is assumed that the low gear ratio is 3.0, thesecond gear ratio is 1.0, the motor gear ratio is 2.0, and the gear usedduring a revolutions transition is the low gear. The product of gearratios is 3.0×2.0=6.0, not lying between the low gear ratio and thesecond gear ratio. In this case, therefore, it is impossible to decreasethe motor output. If the second gear is used during a revolutionstransition, the product of gear ratios is 1.0×2.0=2.0, justcorresponding to half of the low and second gear ratios, so that themotor output is one half and thus can be changed.

Also with respect to the other shift ranges, if no distinction is madeas to which of the procedures is to be adopted, all the shifts toadjacent ranges (e.g., 3-2 shift and 3-4 shift if the automobile isrunning at the third gear) can be done in accordance with the foregoingcontrol procedure. Furthermore, for example, in the case of 2-3 shift,which is an up-shift, the shift is performed in accordance with theprocedure of 1-2 up-shift. However, since the shift is from the secondto the first intermediate shaft, there inevitably is a difference ofgears and the first and the second are reversed with respect to theshafts.

Thus, since the motor output can be changed by the product of gearratios during a shift, the gear ratio of the motor gear used is changedso as to permit an optimum shift. If this gear ratio is set in the rangeof about 1.0 to 1.5, the invention is applicable to almost all theautomobiles available on the market.

Although the above description premises that the direct-coupling gear isused at a gear ratio of 1:1, the motor torque at the start-up of theengine can be decreased by making the direct-coupling gear have a gearratio other than 1:1. For example, if the motor gear ratio is set at 1.4and the direct-coupling gear ratio at about 1.2, the torque of the motorwhich starts the engine at 50 Nm becomes about 74 Nm. Thus, 51 Nm can bedecreased in comparison with the case where the direct-coupling gearratio is set at 1.0.

Also in the case of a coast down shift, the algorithm of FIG. 8 can beused as it is. Although the direction of torque is reverse to that shownin FIG. 9, it is the same if a negative torque is taken into account.The operations of the claw clutches are also the same.

Steps 1 a to 1 c are just the same as in the pedal depressingdown-shift.

If the motor torque is increased in a positive direction (a direction inwhich the torque serves as a braking force for the output shaft toassist the engine output) in Step 2 a, a negative torque of the low gearincreases, while a negative torque of the second gear decreases. This isa torque transition process called torque phase.

Since this torque transition is from the intermediate shaft 17 to theintermediate shaft 13 and the value of the motor torque Tm is madenegative, the input torque of the low gear 14 increases, while the inputtorque of the second gear 18 decreases. When the motor torque Tm reaches−Te, T1 becomes zero and T2 becomes equal to Te.

In Step 2 b, the shift controller 8 determines the end of torque phase.

In Step 2 c, the dog clutch 103 is operated to disengage thedirect-coupling gear 102. In Step 3 a, the dog clutch 103 is furtheroperated to engage the direct-coupling gear 101. Since T1 is zero, thedisengagement can be done easily without causing any change in theoperation of the transmission.

Upon disengagement of the direct-coupling gear 102, the engine speedbecomes changeable.

In Step 4 a, when the shift controller 8 issues a motor speed changecommand, the engine speed changes toward an input number of revolutionsof the low gear. This is a revolutions transition process called inertiaphase.

In the case of 2→1 coast down shift, if the motor speed is increased,the rotational direction reverses and the motor speed rises in apositive direction.

In Step 4 b, the shift controller 8 determines the end of inertia phaseby detecting a synchronized state of the engine speed with the inputnumber of revolutions of the subsequent gear.

In Step 4 c, the dog clutch 22 is operated to engage the claw clutch ofthe low gear 14. Because of the synchronized state, the claw clutch canbe engaged easily without causing any change in the operation of thetransmission.

In Step 5 a, the shift controller 8 issues a motor torque decreasingcommand, making the motor torque zero, whereupon the engine torque Tewhich has been transferred to the second gear 18 through the motor 5shifts to the low gear 14.

In Step 5 b, the shift controller 8 determines the end of the secondtorque phase by detecting that the motor torque Tm is zero.

In Step 5 c, the shift controller 8 operates the dog clutch 113 todisengage the motor gear 112 and the second gear 18 and terminates theshifting. Since Tm is zero, the disengagement can be done easily withoutcausing any change in the operation of the transmission.

As will be seen from the above, the only difference from the pedaldepressing down-shift is that the direction of torque is reverse. Therelation of the number of revolutions is just the same.

In connection with FIGS. 5 to 10, reference has been made to an exampleof how to make a shift to adjacent shift ranges. According to thismethod, it is also possible to make a jump shift. FIG. 11 refers to anexample of 4→2 pedal depressing down-shift, showing changing torquetransfer paths and operations of claw clutches.

(a) shows a state in which the automobile is running at the fourth gear.

In (b), the motor speed is synchronized with the rotational speed of thefirst intermediate shaft 13 to engage the motor gear 111.

By controlling the motor speed so as to become equal to (the rotationalspeed of the intermediate shaft 13)×(gear ratio of the motor gear 111),the third gear 15 can be engaged when the relative rotational speed ofthe dog clutch 22 becomes zero.

As in (c), two torque transfer paths are formed. When the motor torqueis applied, as in the foregoing down shift, the transfer torque shiftsfrom the second to the first intermediate shaft to disengage the fourthgear 19.

In (d), the torque imposed on the shaft of the shifting power unitbecomes the product of the third gear ratio and the motor gear ratio.The motor output can be decreased by setting this product at a valuebetween the second and third gear ratios. Further, if the motor torqueis increased to the rising side of the engine speed, the transmissiongear ratio changes from the fourth gear toward the second gear.

In (e), upon reaching the second gear ratio, the second gear 18 isengaged by the dog clutch 23. The engagement is shock-free because of asynchronized rotation.

In (f), the motor gear 112 and the third gear 15 are disengaged toterminate the shift.

It is seen that even if the gear ranges to be shifted are away from eachother like the second gear and the fourth gear, the shift can be donethrough the first intermediate shaft from the second intermediate shaftwith use of the motor gear 111 or 112.

For example in the conventional twin clutch transmission, a jump shiftrequires cutting off the torque because it is impossible to make apower-on shift. However, according to the method of this embodiment, ashift can be done in a perfect manner and therefore the drivability isimproved.

The following outstanding effects can be obtained by the method of thisembodiment.

The motor output required at the time of performing a shift isrepresented as follows:Pm=|N1−N2|×Te  (Eq. 5)

The energy required for a shift is represented by Pm×time. When themotor speed and the motor torque are different such that one is positiveand the other is negative, this state is a state of regeneration, inwhich the battery is charged. On the other hand, when both motor speedand motor torque are positive or negative, electric power is suppliedfrom the battery. That is, in the case of a power-on up-shift, thebattery is charged in the first half of the shift and is discharged inthe latter half of the shift. Conversely, in the case of a pedaldepressing down-shift, the battery is discharged in the first half ofthe shift, while in the latter half of the shift the battery is charged.Also in the case of a pedal return up-shift and a coast down-shift, bothcharge and discharge are performed during one shift. Thus, when oneshift is over, the battery reverts to its original stage. It followsthat the battery capacity necessary for a shift may be a capacity ableto charge and discharge the energy for one shift.

In a conventional, similar, motor-driven shift method, all of one shiftlies in the charge region in the case of an up-shift, while it lies inthe discharge region in the case of a down-shift. Therefore, if anup-shift is performed up to the fifth gear, followed by a down-shift tothe low gear, it follows that charging is performed five times andthereafter discharging is performed five times, thus requiring a batterycapacity of five times as much. In contrast therewith, in the method ofthis embodiment, a one-tenth battery capacity suffices and thus anoutstanding economical effect is obtained.

According to the system disclosed in Japanese Patent Application No.2002-3561245 filed by the applicant in the present case, in the case ofa transmission having six forward ranges and one reverse range, as largeas twenty-seven gears, seven dog clutches and seven actuators arerequired even if gears provided on an output shaft are made common. Incontrast therewith, in the present invention, twenty-one gears, six dogclutches and six actuators suffice and thus a more outstandingeconomical effect can be attained. This difference in the number ofconstituent elements becomes more significant as the number of gearranges increases. In the manual transmission, the shift ranges have sofar increased like 3rd→4th→5th→6th. A certain truck has shift rangesexceeding ten. Also in the case of automatic transmissions, one havingsix shift ranges has recently been developed. Taking such a recenttrend, it can easily been seen that the present invention is veryimportant.

Thus, in the present invention, a shift can be done while suppressingthe number of constituent elements and the output of the shifting powerunit.

Further, as shown in FIG. 12, by providing a mechanism for fixing thefirst intermediate shaft, the vehicle can be allowed to run with theoutput of the shifting power unit while the vehicular drive system isleft OFF. The following description is now provided about the operationwith reference to FIG. 12.

First, the shift gear 18, the motor gear 112, and the direct-couplinggear 101, are engaged. If a dog clutch 501 is engaged with anintermediate shaft rotation fixing device 500, the intermediate shaftdoes not rotate. Therefore, if a negative torque is outputted from themotor, a torque is applied to the input shaft on the engine 1 side in adirection to decrease the rotational speed. Since the input shaft isconnected with the first intermediate shaft which is engaged to theintermediate shaft rotation fixing device 500, the input shaft does notrotate. Consequently, all the motor torque passes through the shift gear18 from the motor gear 112 and is transferred in a direction to increasethe speed of the output shaft 3. As a result, the wheels rotate and thusthe automobile can be started even without starting the engine. If amechanism capable of power transfer and cut-off such as a clutch 400 ismounted on the input shaft, it becomes possible to disengage the clutch400 (cut off power) and let the engine start up during vehicular runningby the motor.

Insofar as the engine has been started, it is possible to make a shiftto the vehicular running by the engine by disengaging the intermediateshaft rotating fixing device 500 and engaging the clutch 400, becausethere assumes a state of 1-2 shift. As the clutch 400, not only afriction clutch but also a dog clutch or a retarder are employable.

Although in the above embodiment the shifting power unit is constitutedby the motor and the planetary gear mechanism, there may be used afriction clutch as shown in FIG. 13(a). If all the gear ratios of thedirect-coupling gears 101, 102 and the motor gears 111, 112 are set at1:1, the rotational speed of the two shafts of the shifting power unitis certain to become zero when the intermediate shaft reaches the gearratio of the next shift range. Thus, by making engagement with use of afriction gear, it is possible to make a shift to a target gear. In thiscase, deterioration of durability is unavoidable, but the cost can bemade lower than in the use of the motor. If there is used a mechanismcalled retarder which is used in an electric brake, it is possible toeffect a smooth electric control under a reduced influence of friction.The retarder cannot control the rotational speed up to zero andtherefore, if a speed increasing device is provided on the input shaftof the shifting power unit to surely create a rotational difference, asshown in FIG. 13(b), the above electric control can be attained.Moreover, since positive and negative rotational speeds are inputted toboth shafts of the shifting power unit, it is necessary the rotatingdirection of the speed increasing device is made reversible. Therefore,the control in question can be implemented by connecting a dog clutch231 and a normal gear 205 and a reverse gear 206 to a retarder 203 as inFIG. 13(b) and making control through a retarder controller 204.

1. A vehicular drive system comprising: a vehicle driving power unit; ashifting power unit having two rotary shafts; an input shaft connectedto the vehicle driving power unit; two input gears mounted on the inputshaft and capable of being engaged with and disengaged from the inputshaft; a first intermediate shaft; a first driven gear mounted on thefirst intermediate shaft and meshing with one of the input gears; asecond intermediate shaft; a second driven gear mounted on the secondintermediate shaft and meshing with the other input gear; a first shiftgear train mounted on the first intermediate shaft and capable of beingengaged with and disengaged from the first intermediate shaft; a secondshift gear train mounted on the second intermediate shaft and capable ofbeing engaged with and disengaged from the second intermediate shaft; athird driven gear train meshing with the first and second shift geartrains; and an output shaft connected in common to the third driven geartrain, wherein one shaft of the shifting power unit is connected to thevehicle driving power unit and the other shaft of the shifting powerunit is connected to the first and second intermediate shaftsselectively through gears.